This invention relates to an internal combustion engine of the type having opposed pistons operating in axially spaced relation within common power cylinders. The general layout and organization of such an engine is shown and described in my prior U.S. Pat. No. 3,847,124 issued 12 Nov. 1974. A common combustion cylinder receives the opposed heads of the pistons and with them defines a space (e.g. a power cylinder) within which occurs a cycle of compression, ignition, combustion, and expansion. One piston controls exhaust ports, and is generally referred to as the exhaust control piston; the other piston controls air injection and fuel-air charge injection ports, and is generally referred to as the charge control piston.
Preferably, this cycle occurs every stroke of the pistons according to the familiar two-cycle process. The pistons operate separate charging pistons. This is preferably done by forming larger annular charging pistons attached to, or integral with, the main pistons (e.g. providing stepped pistons), and providing charging cylinders coaxial with the main or combustion cylinders but of greater diameter, located at opposite ends of each combustion cylinder. A air-fuel charge is introduced into two of the charging cylinders during the power stroke of the pistons. That gas is compressed in one of the charging cylinders during the compression stroke of the pistons and is transferred to the opposite combustion cylinder through appropriate cross-ducts or passages. The other charging cylinder compresses air alone, and its output is directed to the other combustion cylinder through additional cross passages for supercharging purposes. The difference in volumes of one combustion cylinder and the total volume of the two corresponding charging cylinders determines the amount of supercharge available from a given mechanical design.
The engine preferably includes at least a pair of such compound cylinder assemblies in each of which two pistons operate. The two sets of pistons are connected to a common crank so as to operate 180.degree. out of phase. Thus when one of the cylinder assemblies has fired and the products of combustion in the main cylinder of the other cylinder assembly are being exhausted through an exhaust port, compressed air is directed into that main cylinder, across the head of the charge control piston, from a charging cylinder of the other cylinder assembly to purge products of combustion. Then a fuel-air charge is injected into that main cylinder from the other of the charging cylinders in the other cylinder assembly, to be fired as the cycle advances.